The present invention relates to the field of nonvolatile memory. Specifically, embodiments of the present invention relate enhancing the operational characteristics of a memory device by manipulating the Fermi energy levels in the substrate and in the floating gate portions of the memory device.
Flash memory, which is sometimes called xe2x80x9cflash RAMxe2x80x9d, is a type of non-volatile memory that can be erased and reprogrammed in units of memory called blocks. It is a variation of electrically erasable programmable read-only memory which, unlike flash memory, is erased and rewritten at the byte level, which is slower than flash memory updating. Flash memory is often used to hold control code such as Basic Input/Output System (BIOS) in a personal computer. When BIOS needs to be changed, the flash memory can be written to in block, rather than byte, sizes, making it easy and fast to update.
Flash memory is used in digital cellular phones, digital cameras, LAN switches, PC Cards for notebook computers, digital set-up boxes, embedded controllers, and other devices.
Flash memory gets its name from the organization of the microchip, which allows a section of the memory cells to be erased in a single action or xe2x80x9cflashxe2x80x9d. In one approach, the erasure is caused by hot electrons injected from the drain junction, in which electrons pierce through a thin dielectric material, resulting in the removal of an electronic charge from a floating gate associated with each memory cell. The floating gate stores the charge being programmed.
In one approach, programming is achieved by electron charge injection from the channel area of the drain junction. Although programming is achieved in the conventional floating gate memory, in certain devices programming is not readily conducted, as it is difficult to move electrons between the substrate and the floating gate. This difficulty in the electrons moving between the substrate and the floating gate region adversely affects the programming efficiency. Therefore, the use of the conventional floating gate memory is non-ideal. Accordingly, what is needed is a floating gate memory that can be programmed more easily than the conventional floating gate memory.
The present invention provides a method and device that can achieve greater memory programmability than that of the conventional floating gate memory of the background art.
In various embodiments, the present invention presents a method for enhancing the operational characteristics of a memory device that comprises manipulating the Fermi energy level of a floating gate portion of the memory device such that the floating gate portion attains a first Fermi energy level. Additionally, the Fermi energy level of a substrate portion of the memory device is manipulated such that the substrate portion attains a second Fermi energy level, wherein the first and second Fermi energy levels differ such that the movement of electrons between the substrate and the floating gate is readily facilitated.
In one embodiment, the manipulation of the Fermi energy level of the floating gate is accomplished through fabricating the floating gate of a material comprising an undoped polysilicon material. In one embodiment, the manipulation of the Fermi energy level of the floating gate is accomplished through fabricating the floating gate of a material comprising an undoped polysilicon germanium material.
In another embodiment, the manipulation of the Fermi energy level of the floating gate is accomplished through fabricating the floating gate of a material comprising a p-type doped polysilicon material. In yet another embodiment, the manipulation of the Fermi energy level of the floating gate is accomplished through fabricating the floating gate of a material comprising an p-type doped polysilicon germanium material. In one embodiment, the p-type dopant material is boron.
In one embodiment, the manipulation of the Fermi energy level of the substrate is accomplished through fabricating the substrate of a material comprising a p-type doped polysilicon material.